CHAPTER 16 Air Pollution 359

It is only during the Antarctic spring (September through

December) that conditions are ideal for rapid ozone destruc-

tion. During that season, temperatures are still cold enough for

high-altitude ice crystals, but the sun gradually becomes strong

enough to drive photochemical reactions.

As the Antarctic summer arrives, temperatures moderate

somewhat, the circumpolar vortex breaks down, and air from

warmer latitudes mixes with Antarctic air, replenishing ozone con-

centrations in the ozone hole. Slight decreases worldwide result

from this mixing, however. Ozone re-forms naturally, but not

nearly as fast as it is destroyed. Because the chlorine atoms are

not themselves consumed in reactions with ozone, they continue

to destroy ozone for years. Eventually they can precipitate out, but

this process happens very slowly in the stable stratosphere.

About 10 percent of all stratospheric ozone worldwide has

been destroyed in recent years, and levels over the Arctic have

averaged 40 percent below normal. Ozone depletion has been

observed over the North Pole as well, although it is not as concen-

trated as that in the south.

The Montreal Protocol is a resounding success The discovery of stratospheric ozone losses brought about a

remarkably quick international response. In 1987 an interna-

tional meeting in Montreal, Canada, produced the Montreal

Protocol, the first of several major international agreements

on phasing out most use of CFCs by 2000. As evidence accu-

mulated, showing that losses were larger and more widespread

than previously thought, the deadline for the elimination of all

CFCs (halons, carbon tetrachloride, and methyl chloroform)

was moved up to 1996, and a $500 million fund was established

to assist poorer countries in switching to non-CFC technologies.

Fortunately, alternatives to CFCs for most uses already exist.

The first substitutes are hydrochlorofluorocarbons (HCFCs),

which release much less chlorine per molecule. These HCFCs

are also being phased out, as newer halogen-free alternatives are

developed.

The Montreal Protocol is often cited as the most effective

international environmental agreement ever established. Global

CFC production has been cut by more than 95 percent since 1988

( fig. 16.16 ). Some of that has been replaced by HCFCs, which

release chlorine, but not as much as CFCs. The amount of chlorine

entering the atmosphere already has begun to decrease.

The size of the O 3 “hole” increased steadily from its dis-

covery until the mid-1990s, when the Montreal Protocol began

having an effect. Since then it has varied from year to year, but

the trend has been to stabilize or decrease in recent years. In one

of the world’s most remarkable success stories, stratospheric O 3

levels should be back to normal by about 2049. There is varia-

tion in this trend, however. The 2006 O 3 hole was the largest

ever. Ironically, climate warming in the lower atmosphere has

contributed to cooling in the stratosphere. This cooling increases

ice crystal formation over the Antarctic and results in more

O 3 depletion.

The Montreal Protocol had an added benefit in the fact

that CFCs and other ozone-destroying gases are also powerful,

persistent greenhouse gases. Reductions in emissions of these

gases under the Montreal Protocol amount to one-quarter of all

greenhouse gas emissions worldwide. This reduction is having

a greater impact on climate-changing gases than the Kyoto

Protocol has yet had. Thus the agreements in the Montreal

Protocol are having extended, and very encouraging, positive

effects.

There’s another interesting connection to climate change.

Under the Montreal Protocol, China, India, Korea, and Argentina

were allowed to continue to produce 72,000 tons (combined) of

CFCs per year until 2010. Most of the funds appropriated through

the Montreal Protocol are going to these countries to help them

phase out CFC production and destroy their existing stocks.

Because CFCs are potent greenhouse gases, this phase-out also

makes these countries eligible for credits in the climate trading

market. In 2006 nearly two-thirds of the greenhouse gas emissions

credits traded internationally were for HFC-23 elimination, and

almost half of all payments went to China. Some critics

think this is double-dipping, but if it

eliminates a dangerous risk to all of

us, isn’t it worth it?

In 1995 chemists Sherwood

Rowland, Mario Molina, and

Paul Crutzen shared the Nobel

Prize in Chemistry for their

work on atmospheric chemis-

try and stratospheric ozone.

This was the first Nobel

Prize for an environ-

mental issue.

FIGURE 16.16 The Montreal Protocol has been remarkably

successful in eliminating CFC production. The remaining HFC and

HCFC use is primarily in developing countries, such as China and India.

Table 16.4 Stratospheric Ozone Destruction by Chlorine Atoms and UV Radiation

Step Products

1. CFCl 3 (chlorofluorocarbon) � UV energy CFCl 2 � Cl

2. Cl � O 3 ClO � O 2

3. O 2 � UV energy 2O

4. ClO � 2O O 2 � Cl

5. Return to step 2

360 CHAPTER 16 Air Pollution http://www.mhhe.com/cunningham12e

16.4 Effects of Air Pollution Air pollution is a problem of widespread interest because it

affects so many parts of our lives. The most obvious effects are

on our health. Damage to infrastructure, vegetation, and aesthetic

quality—especially visibility—are also important considerations.

Polluted air damages lungs The World Health Organization estimates that some 5 to 6 million

people die prematurely every year from illnesses related to air pol-

lution. Heart attacks, respiratory diseases, and lung cancer all are

significantly higher in people who breathe dirty air, compared

to matching groups in cleaner environments. Residents of the

most polluted cities in the United States, for example, are 15 to

17 percent more likely to die of these illnesses than those in cities

with the cleanest air. This can mean as much as a five- to ten-year

decrease in life expectancy for those who live in the worst parts

of Los Angeles or Baltimore, compared to a place with clean air.

Of course, the likelihood of suffering ill health from air pollutants

depends on the intensity and duration of exposure as well as age and

prior health status. The very young, the very old, and those already

suffering from respiratory or cardiovascular disease are much more

at risk. Some people are supersensitive because of genetics or prior

exposure. And those doing vigorous physical work or exercise are

more likely to succumb than more sedentary folks.

The United Nations estimates that at least 1.3 billion people

around the world live in areas where outdoor air is dangerously

polluted. Mexico City is among the world’s most polluted cities,

largely because of vehicle exhaust and dust. In Madrid, Spain,

smog is estimated to shave one-half year off the life of each resi-

dent. This adds up to more than 50,000 years lost annually for

the whole city. In China, city dwellers are four to six times more

likely than country folk to die of lung cancer. As noted earlier, the

greatest air quality problem is often in poorly ventilated homes

in poorer countries where smoky fires are used for cooking and

heating. Billions of women and children spend hours each day in

these unhealthy conditions. The World Health Organization esti-

mates that 2 million children under age 5 die each year from acute

respiratory diseases exacerbated by air pollution.

In industrialized countries, one of the biggest health threats

from air pollution is from soot or fine particulate material.

We once thought that particles smaller than 10 micrometers

(10 millionths of a meter) were too small to be trapped in the lungs.

Now we know that fine PM2.5 particles (less than 2.5 micrometers

in diameter) pose even greater risks than coarse particles. They

have been linked with heart attacks, asthma, bronchitis, lung can-

cer, immune suppression, and abnormal fetal development, among

other health problems. Fine particulates have many sources. Until

recently power plants were the largest source, but clean air rules

will require power plants to install filters and precipitators to

remove at least 70 percent of their particulate emissions.

Diesel engines have long been a major source of both soot and

SO 2 in the United States ( fig. 16.17 ). Under a new rule announced

in 2006, new engines in trucks and buses, in combination with

low-sulfur diesel fuel that is now required nationwide, will reduce

particulate emissions by up to 98 percent when the rule is fully

implemented in 2012. These standards will also be applied to

off-road vehicles, such as tractors, bulldozers, locomotives, and

barges, whose engines previously emitted more soot than all the

nation’s cars, trucks, and buses together. The sulfur content of

diesel fuel is now 500 parts per million (ppm) compared to an

average of 3,400 ppm before the regulations were imposed. By

2012 only 15 ppm of sulfur will be allowed in diesel fuel. The U.S. EPA estimates that at least 160 million Americans—

more than half the population—live in areas with unhealthy con-

centrations of fine particulate matter. PM2.5 levels have decreased

about 30 percent over the past 25 years, but health conditions will

improve if we can make further reductions.

How does pollution make us sick? The most common route of exposure to air pollutants is by inha-

lation, but direct absorption through the skin or contamination

of food and water also are important pathways. Because they are

strong oxidizing agents, sulfates, SO 2 , NO x , and O 3 act as irri-

tants that damage delicate tissues in the eyes and respiratory pas-

sages. Fine particulates, irritants in their own right, penetrate deep

into the lungs and carry metals and other HAPs on their surfaces.

Inflammatory responses set in motion by these irritants impair lung

function and trigger cardiovascular problems as the heart tries to

compensate for lack of oxygen by pumping faster and harder. If

the irritation is really severe, so much fluid seeps into the lungs

through damaged tissues that the victim actually drowns.

Carbon monoxide binds to hemoglobin and decreases the abil-

ity of red blood cells to carry oxygen. Asphyxiants such as this cause

headaches, dizziness, and heart stress, and can be lethal if concen-

trations are high enough. Lead also binds to hemoglobin, reducing

its oxygen-carrying capacity at high levels. At lower levels, lead

FIGURE 16.17 Soot and fine particulate material from diesel

engines, wood stoves, power plants, and other combustion

sources have been linked to asthma, heart attacks, and a variety

of other diseases.

CHAPTER 16 Air Pollution 361

causes long-term damage to critical neurons in the brain that results

in mental and physical impairment and developmental retardation.

Some important chronic health effects of air pollutants include

bronchitis and emphysema. Bronchitis is a persistent inflammation

of bronchi and bronchioles (large and small airways in the lung)

that causes mucus buildup, a painful cough, and involuntary muscle

spasms that constrict airways. Severe bronchitis can lead to emphy-

sema, an irreversible chronic obstructive lung disease in which

airways become permanently constricted and alveoli are damaged

or even destroyed. Stagnant air trapped in blocked airways swells

the tiny air sacs in the lung (alveoli), blocking blood circulation. As

cells die from lack of oxygen and nutrients, the walls of the alveoli

break down, creating large empty spaces incapable of gas exchange

( fig. 16.18 ). Thickened walls of the bronchioles lose elasticity, and

breathing becomes more difficult. Victims of emphysema make a

characteristic whistling sound when they breathe. Often they need

supplementary oxygen to make up for reduced respiratory capacity. Irritants in the air are so widespread that about half of all lungs

examined at autopsy in the United States have some degree of alve-

olar deterioration. The Office of Technology Assessment (OTA)

estimates that 250,000 people suffer from pollution-related bronchi-

tis and emphysema in the United States, and some 50,000 excess

deaths each year are attributable to complications of these diseases,

which are probably second only to heart attack as a cause of death.

Smoking is undoubtedly the largest cause of obstructive lung

disease and preventable death in the world. The World Health

Organization says that tobacco kills some 3 million people each

year. This ranks it with AIDS as one of the world’s leading kill-

ers. Because of cardiovascular stress caused by carbon monoxide

in smoke and chronic bronchitis and emphysema, about twice as

many people die of heart failure as die from lung cancer associ-

ated with smoking. The Surgeon General estimates that more than

400,000 people die each year in the United States from emphy-

sema, heart attacks, strokes, lung cancer, or other diseases caused

by smoking. These diseases are responsible for 20 percent of all

mortality in the United States, or four times as much as infectious

agents. Lung cancer has now surpassed breast cancer as the lead-

ing cause of cancer deaths for U.S. women. Advertising aimed at

making smoking appear stylish and liberating has resulted in

a 600 percent increase in lung cancer among women since 1950.

Total costs for early deaths and smoking-related illnesses in the

United States are estimated to be $100 billion per year.

Plants suffer cell damage and lost productivity Uncontrolled industrial fumes from furnaces, smelters, refiner-

ies, and chemical plants destroy vegetation and created desolate,

barren landscapes around mining and manufacturing centers.

The copper-nickel smelter at Sudbury, Ontario, is a spectacular

and notorious example of air pollution effects on vegeta-

tion and ecosystems. In 1886 the corporate ancestor of the

International Nickel Company (INCO) began open-bed roasting of

sulfide ores at Sudbury. Sulfur dioxide and sulfuric acid released

by this process caused massive destruction of the plant commu-

nity within about 30 km of the smelter. Rains washed away the

exposed soil, leaving a barren moonscape of blackened bedrock

( fig. 16.19 a ). Super-tall, 400 m smokestacks were installed in the

1950s, and sulfur scrubbers were added 20 years later. Emissions

were reduced by 90 percent and the surrounding ecosystem is

beginning to recover ( fig. 16.19 b ). Similar destruction occurred

at many other sites during the nineteenth century. Copperhill,

Tennessee, Butte, Montana, and the Ruhr Valley in Germany are

some well-known examples, but these areas also are showing

signs of recovery since corrective measures were taken. Norilsk,

Russia, is a copper-smelting town that continues to have these

extremely barren conditions. Norilsk’s far northern latitude puts

struggling vegetation at a further disadvantage, and its remote

location minimizes public oversight, making conditions even

more persistent than in many other smelting areas. There are two probable ways that air pollutants damage

plants. They can be directly toxic, damaging sensitive cell mem-

branes much as irritants do in human lungs. Within a few days

of exposure to toxic levels of oxidants, mottling (discoloration)

occurs in leaves due to chlorosis (bleaching of chlorophyll), and

then necrotic (dead) spots develop ( fig. 16.5 ). If injury is severe,

the whole plant may be killed. Sometimes these symptoms are so

distinctive that positive identification of the source of damage is

possible. Often, however, the symptoms are vague and difficult to

separate from diseases or insect damage.

Certain combinations of environmental factors have syner-gistic effects in which the injury caused by exposure to two

factors together is more than the sum of exposure to each factor

individually. For instance, when white pine seedlings are exposed

to subthreshold concentrations of ozone and sulfur dioxide indi-

vidually, no visible injury occurs. If the same concentrations of

pollutants are given together, however, visible damage occurs.

In alfalfa, however, SO 2 and O 3 together cause less damage than

Bronchial musclein spasm

Buildup of mucus inthe bronchial tube

Overinflated alveolidue to trapped air

Bronchial muscle

Bronchial tube

Normal alveoli

FIGURE 16.18 Bronchitis and emphysema can result in con-

striction of airways and permanent damage to tiny, sensitive air

sacs called alveoli, where oxygen diffuses into blood vessels.

362 CHAPTER 16 Air Pollution http://www.mhhe.com/cunningham12e

either one alone. These complex interactions point out the unpre-

dictability of future effects of pollutants. Outcomes might be either

more or less severe than previous experience indicates.

Pollutant levels too low to produce visible symptoms of damage

may still have important effects. Field studies using open-top cham-

bers ( fig. 16.20 ) and charcoal-filtered air show that yields in some sen-

sitive crops, such as soybeans, may be reduced as much as 50 percent

by currently existing levels of oxidants in ambient air. Some plant

pathologists suggest that ozone and photochemical oxidants are

responsible for as much as 90 percent of agricultural, ornamental, and

forest losses from air pollution. The total costs of this damage may be

as much as $10 billion per year in North America alone.

Acid deposition has many negative effects Most people in the United States became aware of problems asso-

ciated with acid precipitation (the deposition of wet acidic solu-

tions or dry acidic particles from the air) within the last decade

or so, but English scientist Robert Angus Smith coined the term

acid rain in his studies of air chemistry in Manchester, England,

in the 1850s. By the 1940s it was known that pollutants, including

atmospheric acids, could be transported long distances by wind

currents. This was thought to be only an academic curiosity until it

was shown that precipitation of these acids can have far-reaching

ecological effects.

We describe acidity in terms of pH (see figure 3.4). Values

below 7 are acidic, while those above 7 are alkaline. Normal,

unpolluted rain generally has a pH of about 5.6 due to carbonic

acid created by CO 2 in air. Sulfur, chlorine, and other elements

also form acidic compounds as they are released in sea spray,

volcanic emissions, and biological decomposition. These sources

can lower the pH of rain well below 5.6. Other factors, such as

alkaline dust can raise it above 7. In industrialized areas, anthro-

pogenic acids in the air usually far outweigh those from natu-

ral sources. Acid rain is only one form in which acid deposition

occurs. Fog, snow, mist, and dew also trap and deposit atmo-

spheric contaminants. Furthermore, fallout of dry sulfate, nitrate,

and chloride particles can account for as much as half of the

acidic deposition in some areas.

Aquatic Effects Lakes and streams can be especially sensitive to acid deposi-

tion, especially where vegetation or bedrock makes them naturally

acidic to start with. This problem was first publicized in Scandinavia,

which receives industrial and auto mobile emissions — principally

H 2 SO 4 and HNO 3 —generated in northwestern Europe. The thin,

acidic soils and oligotrophic lakes and streams in the mountains of

southern Norway and Sweden have been severely affected by this

acid deposition. Some 18,000 lakes in Sweden are now so acidic

that they will no longer support game fish or other sensitive aquatic

organisms.

Generally, reproduction is the most sensitive stage in fish

life cycles. Eggs and fry of many species are killed when the pH

drops to about 5.0. This level of acidification also can disrupt the

food chain by killing aquatic plants, insects, and invertebrates on

FIGURE 16.20 An open-top chamber tests air pollution

effects on plants under normal conditions for rain, sun, field soil,

and pest exposure.

FIGURE 16.19 In 1975, acid precipitation from the copper-nickel smelters (tall stacks in background) had killed all the vegetation and

charred the pink granite bedrock black for a large area around Sudbury, Ontario (a). By 2005, forest cover was growing again, although the

rock surfaces remain burned black (b).

(a) 1975 (b) 2005

CHAPTER 16 Air Pollution 363

FIGURE 16.21 Acid precipitation over the United States. Source: National Atmospheric Deposition Program/National Trends Network, 2000. http://nadp.sws.uiuc.edu.

Buildings and Monuments In cities throughout the world, some of the oldest and most glori-

ous buildings and works of art are being destroyed by air pollution.

Smoke and soot coat buildings, paintings, and textiles. Limestone

and marble are destroyed by atmospheric acids at an alarming rate.

The Parthenon in Athens, the Taj Mahal in Agra, the Colosseum

in Rome, frescoes and statues in Florence, medieval cathedrals in

Europe ( fig. 16.23 ), and the Lincoln Memorial and Washington

Monument in Washington, D.C., are slowly dissolving and flak-

ing away because of acidic fumes in the air. Medieval stained glass

windows in Cologne’s gothic cathedral are so porous from etching

by atmospheric acids that pigments disappear and the glass literally

crumbles away. Restoration costs for this one building alone are

estimated at 1.5 to 3 billion euros (U.S. $1.8 billion). On a more mundane level, air pollution also damages ordinary

buildings and structures. Corroding steel in reinforced concrete

weakens buildings, roads, and bridges. Paint and rubber deterio-

rate due to oxidation. Limestone, marble, and some kinds of sand-

stone flake and crumble. The Council on Environmental Quality

estimates that U.S. economic losses from architectural damage

caused by air pollution amount to about $4.8 billion in direct costs

and $5.2 billion in property value losses each year.

Smog and haze reduce visibility We have realized only recently that pollution affects rural areas

as well as cities. Even supposedly pristine places like our national

parks are suffering from air pollution. Grand Canyon National Park,

where maximum visibility used to be 300 km, is now so smoggy

on some winter days that visitors can’t see the opposite rim only

20 km across the canyon. Mining operations, smelters, and power

plants (some of which were moved to the desert to

which fish depend for food. At pH levels below 5.0, adult fish

die as well. Trout, salmon, and other game fish are usually the

most sensitive. Carp, gar, suckers, and other less desirable fish are

more resistant.

In the early 1970s, evidence began to accumulate suggesting

that air pollutants are acidifying many lakes in North America.

Studies in the Adirondack Mountains of New York revealed that

about half of the high-altitude lakes (above 1,000 m or 3,300 ft)

were acidified and had no fish. Areas showing lake damage cor-

relate closely with average pH levels in precipitation ( fig. 16.21 ).

Some 48,000 lakes in Ontario are endangered, and nearly all of

Quebec’s surface waters, including about 1 million lakes, are

believed to be highly sensitive to acid deposition. Sulfates account for about two-thirds of the acid deposition

in eastern North America and most of Europe, while nitrates con-

tribute most of the remaining one-third. In urban areas, where

transportation is the major source of pollution, nitric acid is

equal to or slightly greater than sulfuric acids in the air. A vigor-

ous program of pollution control has been undertaken by both

Canada and the United States, and SO 2 and NO x emissions have

decreased dramatically over the past three decades over much of

North America.

Forest Damage In the early 1980s, disturbing reports appeared of rapid forest

declines in both Europe and North America. One of the earliest

was a detailed ecosystem inventory on Camel’s Hump Mountain

in Vermont. A 1980 survey showed that seedling production,

tree density, and viability of spruce-fir forests at high eleva-

tions had declined about 50 percent

in 15 years. A similar situation

was found on Mount Mitchell in

North Carolina, where almost all

red spruce and Fraser fir above

2,000 m (6,000 ft) are in a

severe decline. Nearly all the

trees are losing needles and

about half of them are dead

( fig. 16.22 ). The stress of acid

rain and fog, other air pollut-

ants, and attacks by an invasive

insect called the woody aldegid

are killing the trees. Many European countries re-

ported catastrophic forest destruction

in the 1980s. It still isn’t clear what caused this

injury. In the longest-running forest-ecosystem

monitoring record in North America, researchers at the Hubbard

Brook Experimental Forest in New Hampshire have shown that

forest soils have become depleted of natural buffering reserves of

basic cations such as calcium and magnesium through years of

exposure to acid rain. Replacement of these cations by hydrogen

and aluminum ions seems to be one of the main causes of plant

mortality.

364 CHAPTER 16 Air Pollution http://www.mhhe.com/cunningham12e

improve air quality in cities like Los Angeles) are the main culprits.

Similarly, the vistas from Shenandoah National Park just outside

Washington, D.C., are so hazy that summer visibility is often less

than 1.6 km because of smog drifting in from nearby urban areas.

Historical records show that over the past four or five decades

human-caused air pollution has spread over much of the United

States. Researchers report that a gigantic “haze blob” as much

as 3,000 km across covers much of the eastern United States in

the summer, cutting visibility as much as 80 percent. Smog and

haze are so prevalent that it’s hard for people to believe that the air

once was clear. Studies indicate, however, that if all human-made

sources of air pollution were shut down, the air would clear up in a

few days and there would be about 150 km visibility nearly every-

where rather than the 15 km to which we have become accustomed.

16.5 Air Pollution Control “Dilution is the solution to pollution” was one of the early

approaches to air pollution control. Tall smokestacks were built to

send emissions far from the source, where they became unidentifi-

able and largely untraceable. But dispersed and diluted pollutants

are now the source of some of our most serious pollution problems.

We are finding that there is no “away” to which we can throw our

waste products. While most of the discussion in this section focuses

on industrial solutions, each of us can make important personal

contributions to this effort (What Can You Do? p. 365). Because most air pollution in the developed world is associ-

ated with transportation and energy production, the most effective

strategy would be conservation: Reducing electricity consump-

tion, insulating homes and offices, and developing better public

transportation could all greatly reduce air pollution in the United

States, Canada, and Europe. Alternative energy sources, such as

wind and solar power, produce energy with little or no pollution,

and these and other technologies are becoming economically com-

petitive (chapter 20). In addition to conservation, pollution can be

controlled by technological innovation.

Substances can be captured after combustion Particulate removal involves filtering air emissions. Filters trap

particulates in a mesh of cotton cloth, spun glass fibers, or asbestos-

cellulose. Industrial air filters are generally giant bags 10 to 15 m

long and 2 to 3 m wide. Effluent gas is blown through the bag,

much like the bag on a vacuum cleaner. Every few days or weeks,

the bags are opened to remove the dust cake. Electrostatic pre-

cipitators are the most common particulate controls in power

plants. Ash particles pick up an electrostatic surface charge as they

pass between large electrodes in the effluent stream ( fig. 16.24 ).

FIGURE 16.23 Atmospheric acids, especially sulfuric and

nitric acids, have almost completely eaten away the face of this

medieval statue. Each year the total loss from air pollution dam-

age to buildings and materials amounts to billions of dollars.

FIGURE 16.22 A Fraser fir forest on Mount Mitchell, North

Carolina, killed by acid rain, insect pests, and other stressors.

Cleaned gasElectrodes

Dirty gasDust discharge

FIGURE 16.24 An electrostatic precipitator traps particulate

material on electrically charged plates as effluent makes its way to

the smokestack.

CHAPTER 16 Air Pollution 365

Charged particles then collect on an oppositely charged collecting

plate. These precipitators consume a large amount of electricity,

but maintenance is relatively simple, and collection efficiency can

be as high as 99 percent. The ash collected by both of these tech-

niques is a solid waste (often hazardous due to the heavy metals

and other trace components of coal or other ash source) and must

be buried in landfills or other solid-waste disposal sites. Sulfur removal is important because sulfur oxides are among

the most damaging of all air pollutants in terms of human health

and ecosystem viability. Switching from soft coal with a high sul-

fur content to low-sulfur coal is the surest way to reduce sulfur

emissions. High-sulfur coal is frequently politically or economi-

cally expedient, however. In the United States, Appalachia, a

region of chronic economic depression, produces most high-sulfur

coal. In China, much domestic coal is rich in sulfur. Switching

to cleaner oil or gas would eliminate metal effluents as well as

sulfur. Cleaning fuels is an alternative to switching. Coal can be

crushed, washed, and gasified to remove sulfur and metals before

combustion. This improves heat content and firing properties, but

may replace air pollution with solid-waste and water pollution

problems; furthermore, these steps are expensive.

Sulfur can also be removed to yield a usable product instead

of simply a waste disposal problem. Elemental sulfur, sulfuric

acid, and ammonium sulfate can all be produced using catalytic

converters to oxidize or reduce sulfur. Markets have to be reason-

ably close and fly ash contamination must be reduced as much as

possible for this procedure to be economically feasible.

Nitrogen oxides (NO x ) can be reduced in both internal com-

bustion engines and industrial boilers by as much as 50 percent

by carefully controlling the flow of air and fuel. Staged burners,

for example, control burning temperatures and oxygen flow to pre-

vent formation of NO x . The catalytic converter on your car uses

platinum-palladium and rhodium catalysts to remove up to 90 per-

cent of NO x , hydrocarbons, and carbon monoxide at the same time.

Hydrocarbon controls mainly involve complete combustion

or controlling evaporation. Hydrocarbons and volatile organic

compounds are produced by incomplete combustion of fuels or by

solvent evaporation from chemical factories, paints, dry cleaning,

plastic manufacturing, printing, and other industrial processes.

Closed systems that prevent escape of fugitive gases can reduce

many of these emissions. In automobiles, for instance, positive

crankcase ventilation (PCV) systems collect oil that escapes from

around the pistons and unburned fuel and channels them back

to the engine for combustion. Controls on fugitive losses from

industrial valves, pipes, and storage tanks can have a significant

impact on air quality. Afterburners are often the best method for

destroying volatile organic chemicals in industrial exhaust stacks.

Fuel switching and fuel cleaning cut emissions Switching from soft coal with a high sulfur content to low-sulfur

coal can greatly reduce sulfur emissions. In the United States most

high-sulfur coal comes from Appalachia, while low-sulfur coal

comes mainly from Wyoming, Montana, and other western states.

Because Appalachian economies have been heavily dependent on

coal mining for generations, discussions of switching fuel sources

can be highly political. Changing to another fuel, such as natural

gas or nuclear energy, can eliminate all sulfur emissions as well as

those of particulates and heavy metals. Natural gas is more expen-

sive and more difficult to ship and store than coal, however, and

many people prefer the known risks of coal pollution to the uncer-

tain dangers and costs of nuclear power (chapter 19).

Alternative energy sources, such as wind and solar power, are

a more complete form of fuel switching. Alternatives are becom-

ing economically competitive in many areas (chapter 20).

Clean air legislation remains controversial Since 1970 the Clean Air Act has been modified, updated, and amended

many times. Amendments have involved acrimonious debate. As in

the case of CO 2 restrictions, discussed earlier, victims of air pollution

demand more protection, while industry and energy groups insist that

controls are too expensive. Bills have sometimes languished in

Congress for years because of disputes over burdens of responsibility,

cost, and definitions of risk. A 2002 report concluded that simply by

Saving Energy and Reducing Pollution

• Conserve energy: carpool, bike, walk, use public transport, and

buy compact fluorescent bulbs and energy-efficient appliances

(see chapter 20 for other suggestions).

• Don’t use polluting two-cycle gasoline engines if cleaner four-

cycle models are available for lawnmowers, boat motors, etc.

• Buy refrigerators and air conditioners designed for CFC alterna-

tives. If you have old appliances or other CFC sources, dispose

of them responsibly.

• Plant a tree and care for it (every year).

• Write to your congressional representatives and support a transi-

tion to an energy-efficient economy.

• If green-pricing options are available in your area, buy renewable

energy.

• If your home has a fireplace, install a high-efficiency, clean-

burning, two-stage insert that conserves energy and reduces pol-

lution up to 90 percent.

• Have your car tuned every 10,000 miles (16,000 km) and make sure

that its anti-smog equipment is working properly. Turn off your

engine when waiting longer than one minute. Start trips a little

earlier and drive slower—it not only saves fuel but it’s safer, too.

• Use latex-based, low-VOC paint rather than oil-based (alkyd)

paint.

• Avoid spray-can products. Light charcoal fires with electric start-

ers rather than petroleum products.

• Don’t top off your fuel tank when you buy gasoline; stop when

the automatic mechanism turns off the pump. Don’t dump gaso-

line or used oil on the ground or down the drain.

• Buy clothes that can be washed rather than dry-cleaned.

What Can You Do? WWWWWWWWWWWWWWWWWWWhhhhhhhhhhhhhhhhhhhaaaaaaaaaaaaaaaatttttttttttttttttttttt CCCCCCCCCCCCCCCaaaaaaaaaaaaaaaannnnnnnnnnnnnnnnnnn YYYYYYYYYYYYYYYYooooooooooooouuuuuuuuuuuuuuuuuuu DDDDDDDDDDDDDDDDDoooooooooooo?????????????

366 CHAPTER 16 Air Pollution http://www.mhhe.com/cunningham12e

existing clean air legislation, the United States could prevent at least

6,000 deaths and 140,000 asthma attacks every year.

The most significant amendments were in the 1990 update,

which addressed a variety of issues, including acid rain, urban air

pollution, and toxic air emissions. These amendments also restricted

ozone-depleting chemicals in accordance with the Montreal Protocol.

One of the most contested aspects of the act has been the

“new source review,” which was established in 1977. This provi-

sion was adopted because industry argued that it would be intoler-

ably expensive to install new pollution-control equipment on old

power plants and factories that were about to close down anyway.

Congress agreed to “grandfather” existing equipment, or exempt it

from new pollution limits, with the stipulation that when they were

upgraded or replaced, more stringent rules would apply. The result

was that owners have kept old facilities operating precisely because

they were exempted from pollution control. In fact, corporations

poured millions into aging power plants and factories, expanding

their capacity, to avoid having to build new ones. Thirty years later,

most of those grandfathered plants are still going strong and con-

tinue to be among the biggest contributors to smog and acid rain.

Clean air legislation has been very successful Despite these disputes, the Clean Air Act has been extremely suc-

cessful in saving money and lives. The EPA estimates that between

1970 and 2010, lead fell 99 percent, SO 2 declined 39 percent, and CO

shrank 32 percent ( fig. 16.25 ). Filters, scrubbers, and precipitators

on power plants and other large stationary sources are responsible

for most of the particulate and SO 2 reductions. Catalytic converters

on cars are responsible for most of the CO and O 3 reductions. For

23 of the largest U.S. cities, air quality now reaches hazardous levels

93 percent less frequently than a decade ago. Forty of the 97 metro-

politan areas that failed to meet clean air standards in the 1980s are

now in compliance, many for the first time in a generation.

The only conventional, “criteria” pollutants that have not

dropped significantly are particulates and NO x . Because auto-

mobiles are the main source of NO x , cities, such as Nashville,

Tennessee, and Atlanta, Georgia, where pollution comes largely

from traffic, still have serious air quality problems. Rigorous pol-

lution controls are having a positive effect on Southern California

air quality. Los Angeles, which had the dirtiest air in the nation for

decades, wasn’t even in the top 20 polluted cities in 2010.

In a 2011 study of the economic costs and benefits of the 1990

Clean Air Act, the EPA found that the direct benefits of air quality

protection by 2020 will be $2 trillion, while the direct costs of imple-

menting those protections was about 1/30th of that, or $65 billion

( fig. 16.26 ). The direct benefits were mainly in prevented costs of

premature illness, death, and work losses (table 16.5). About half of

the direct costs were improvements in cars and trucks, which now

burn cleaner and more efficiently than they did in the past. This

cost has been distributed to vehicle owners, who also benefit from

lower expenditures on fuel. A quarter of costs involved cleaner fur-

naces and pollutant capture at electricity-generating power plants

and other industrial facilities. The remaining costs involved pollu-

tion reductions at smaller businesses, municipal facilities, construc-

tion sites, and other sources. Overall, emission controls have not

dampened economic productivity, despite widespread fears to the

contrary. Emissions of criteria pollutants have declined in recent

decades, whereas economic indicators have grown ( fig. 16.27 ). In addition to these savings, the Clean Air Act has created

thousands of jobs in developing, installing, and maintaining tech-

nology and in monitoring. At a time when many industries are pro-

viding fewer jobs, owing to greater mechanization, jobs have been

Tho

usan

ds o

f met

ric to

ns/y

ear

140,000

120,000

110,000

80,000

20,000

40,000

60,000

0CO

(–31%)NOx

(+10%)VOC

(–42%)PM-10

(+110%)SO2

(–39%)

1970

2005

FIGURE 16.25 Air pollution trends in the United States, 1970

to 1998. Although population and economic activity increased

during this period, emissions of all criteria air pollutants, except for

nitrogen oxides and particulate matter, decreased significantly. Source: Environmental Protection Agency, 2011.

$0

$200

$400

$600

$800

$1,000

$1,200

$1,400

$1,600

$1,800

$2,000

2000 2010 2020

Bill

ion

s

Benefits

Costs

FIGURE 16.26 Direct costs and benefits of Clean Air Act

provisions by 2000, 2010, and 2020, in billions of 2006 dollars. Source: EPA 2011, Clean Air Impacts Summary Report.

CHAPTER 16 Air Pollution 367

most economical ways to reduce emissions, however, utilities have

been able to reach clean air goals for one-tenth that price. A serious

shortcoming of this approach is that while trading has resulted in

overall pollution reduction, some local “hot spots” remain where

owners have found it cheaper to pay someone else to reduce pollu-

tion than to do it themselves.

Particulate matter (mostly dust and soot) is produced by

agriculture, fuel combustion, metal smelting, concrete manufactur-

ing, and other activities. Industrial cities, such as Baltimore, Mary-

land, and Baton Rouge, Louisiana, also have continuing problems.

Eighty-five other urban areas are still considered nonattainment

regions. In spite of these local failures, however, 80 percent of the

United States now meets the National Ambient Air Quality Stan-

dards ( fig. 16.28 ). This improvement in air quality is perhaps the

greatest environmental success story in our history.

16.6 Global Prospects The outlook is not so encouraging in many parts of the world. The

major metropolitan areas of many developing countries are grow-

ing at explosive rates to incredible sizes (chapter 22), and envi-

ronmental quality is abysmal in many of them. In Mexico City,

notorious for bad air, pollution levels exceed WHO health stan-

dards 350 days per year, and more than half of all city children

have lead levels in their blood high enough to lower intelligence

and retard development. Mexico City’s 131,000 industries and

2.5 million vehicles spew out more than 5,500 tons of air pollut-

ants daily. In Santiago, Chile, suspended particulates exceed WHO

standards of 90 mg/m 3 about 299 days per year.

Rapid industrialization and urban growth outpace pollution controls Rapid growth and industrialization in China, India,

and many other parts of the developing world are pro-

ducing emissions much faster than pollution-control

agencies can manage. Because China’s growth is so

rapid, its air quality is increasingly poor. Many of

China’s 400,000 factories have no air pollution con-

trols. Experts estimate that home coal burners and

factories emit 10 million tons of soot and 15 million

tons of sulfur dioxide annually and that emissions

have increased rapidly over the past 20 years. Sixteen

of the 20 cities in the world with the worst air quality

are in China. Shenyang, an industrial city in northern

China, is thought to have the world’s worst continu-

ing particulate problem, with peak winter concen-

trations over 700 mg/m 3 (nine times U.S. maximum

standards). Airborne particulates in Shenyang exceed

WHO standards on 347 days per year. It’s estimated

that air pollution is responsible for 400,000 prema-

ture deaths every year in China. Beijing, Xi’an, and

Guangzhou also have severe air pollution problems.

The high incidence of cancer in Shanghai is thought

to be linked to air pollution (see fig. 16.1 ).

90–50%

–40%

–41%

19%

20%22%

36%

64%

–30%

–20%

–10%

0%

10%

20%

30%

40%

50%

60%

70%

95 96 97 98 99 00 01 02 03 04 05 06 07 08

Aggregateemissions(6 commonpollutants)

Population

Energyconsumption

Vehicle milestraveled

Gross DomesticProduct

CO2 emissions

FIGURE 16.27 Comparison of growth measures and emissions of criteria air

pollutants, 1990–2008. Source: EPA, 2011.

Table 16.5 Reductions of Health Impairments Resulting from Ozone and Particulate Reductions Since 1990

Health Effect Reductions (PM2.5 & Ozone Only)

Year 2010 (in cases)

Year 2020 (in cases)

Adult Mortality-particles 160,000 230,000

Infant Mortality-particles 230 280

Mortality-ozone 4300 7100

Chronic Bronchitis 54,000 75,000

Heart Disease 130,000 200,000

Asthma Exacerbation 1,700,000 2,400,000

Emergency Room Visits 86,000 120,000

School Loss Days 3,200,000 5,400,000

Lost Work Days 13,000,000 17,000,000

Source: EPA, 2011.

growing in clean technologies and pollution control and moni-

toring. At the same time, reductions in acid rain have decreased

losses to forest resources and building infrastructure.

Market mechanisms have been part of the solution, especially

for sulfur dioxide, which is widely considered to have benefited

from a cap-and-trade approach. This strategy sets maximum limits

for each facility and then lets facilities sell pollution credits if they

can cut emissions, or facilities can buy credits if they are cheaper

than installing pollution-control equipment. When trading began

in 1990, economists estimated that eliminating 10 million tons

of sulfur dioxide would cost $15 billion per year. Left to find the

368 CHAPTER 16 Air Pollution http://www.mhhe.com/cunningham12e

Every year the Blacksmith Institute compiles a list of the

world’s worst-polluted places. Globally, smelters, mining opera-

tions, petrochemical industries—which release hazardous organic

compounds to the air and water—and chemical manufacturing are

frequently the worst sources of pollutants. Often these are in impov-

erished and developing areas of Africa, Asia, or the Americas,

where government intervention is weak and regulations are

nonexistent or poorly enforced. Funds and political will are usually

unavailable to deal with pollution, much of which is involved with

materials going to wealthier countries or waste that is received from

developed countries (see chapter 21).You can learn more about

these places at www.blacksmithinstitute.org .

Norilsk, Russia (one site highlighted on Blacksmith Institute’s

list of worst places), is a notorious example of toxic air pollution.

Founded in 1935 as a slave labor camp, this Siberian city is con-

sidered one of the most polluted places on earth. Norilsk houses the

world’s largest nickel mine and heavy metals smelting complex,

which discharge over 4 million tons of cadmium, copper, lead, nickel,

arsenic, selenium, and zinc into the air every year. The snow turns

black as quickly as it falls, the air tastes of sulfur, and the average life

expectancy for factory workers is ten years below the Russian average

(which already is the lowest of any industrialized country). Difficult

pregnancies and premature births are much more common in Norilsk

than elsewhere in Russia. Children living near the nickel plant are ill

twice as much as Russia’s average, and birth defects are reported to

affect as much as 10 percent of the population. Why do people stay in

such a place? Many were attracted by high wages and hardship pay,

and now that they’re sick, they can’t afford to move.

There are also signs of progress Despite global expansion of chemical industries and other sources

of air pollution, there have been some spectacular successes in air

pollution control. Sweden and West Germany (countries affected

by forest losses due to acid precipitation) cut their sulfur emissions

by two-thirds between 1970 and 1985. Austria and Switzerland

have gone even farther, regulating even motorcycle emissions.

The Global Environmental Monitoring System (GEMS) reports

declines in particulate levels in 26 of 37 cities worldwide. Sulfur

dioxide and sulfate particles, which cause acid rain and respiratory

disease, have declined in 20 of these cities.

Even poor countries can control air pollution. Delhi, India,

for example, was once considered one of the world’s ten most

polluted cities. Visibility often was less than 1 km on smoggy

days. Health experts warned that breathing Delhi’s air was equiv-

alent to smoking two packs of cigarettes per day. Pollution levels

were nearly five times higher than World Health Organization

standards. Respiratory diseases were widespread, and the can-

cer rate was significantly higher than for surrounding rural areas.

The biggest problem was vehicle emissions, which contributed

about 70 percent of air pollutants (industrial emissions made up

20 percent, while burning of garbage and firewood made up most

of the rest).

In the 1990s catalytic converters were required for auto-

mobiles, and unleaded gasoline and low-sulfur diesel fuel were

introduced. In 2000 private automobiles were required to meet

European standards, and in 2002 more than 80,000 buses, auto-

rickshaws, and taxis were required to switch from liquid fuels

to compressed natural gas ( fig. 16.29 ). Sulfur dioxide and car-

bon monoxide levels have dropped 80 percent and 70 percent,

respectively, since 1997. Particulate emissions have dropped

by about 50 percent. Residents report that the air is dramati-

cally clearer and more healthy. Unfortunately, rising prosperity,

FIGURE 16.28 Projected visibility impairments, shown with

dark colors, would be considerably worse in 2020 without the

1990 Clean Air Act amendments (CAAA, top ) than they will be

with the amendments (bottom). Units are deciviews, a measure of

perceptible change in visibility. Source: EPA 2011, Clean Air Impacts Summary Report.

CHAPTER 16 Air Pollution 369

FIGURE 16.29 Air quality in Delhi, India, has improved dra-

matically since buses, auto-rickshaws, and taxis were required to

switch from liquid fuels to compressed natural gas. This is one of

the most encouraging success stories in controlling pollution in

the developing world.

FIGURE 16.30 Cubatao, Brazil, was once considered one

of the most polluted cities in the world. Better environmental

regulations and enforcement along with massive investments in

pollution-control equipment have improved air quality significantly.

CONCLUSION Air pollution is often the most obvious and widespread type of

pollution. Everywhere on earth, from the most remote island in

the Pacific, to the highest peak in the Himalayas, to the frigid

ice cap over the North Pole, there are traces of human-made

contaminants, remnants of the 2 billion metric tons of pollutants

released into the air worldwide every year by human activities.

Adverse effects of air pollution include respiratory diseases,

birth defects, heart attacks, developmental disabilities in chil-

dren, and cancer. Environmental impacts include destruction of

stratospheric ozone, poisoning of forests and waters by acid rain,

and corrosion of building materials.

We have made encouraging progress in controlling air pollu-

tion, progress that has economic benefits as well as health benefits.

Many students aren’t aware of how much worse air quality was in

the industrial centers of North America and Europe a century or

two ago compared to today. Cities such as London, Pittsburgh, Chi-

cago, Baltimore, and New York had air quality as bad as or worse

than most megacities of the developing world now. The progress in

reducing air pollution in these cities gives us hope that residents

can do so elsewhere as well.

The success of the Montreal Protocol in eliminating CFCs is

a landmark in international cooperation on an environmental

problem. Growth of the stratospheric ozone hole has slowed, and

we expect the ozone depletion to end in about 50 years. This is

one of the few global environmental threats that has had such a

rapid and successful resolution. Let’s hope that others will follow.

Developing areas face severe challenges in air quality. Most

of the worst air pollution in the world occurs in large cities of

developing countries. However, there are dramatic cases of pol-

lution in developing countries. Problems that once seemed over-

whelming can be overcome. In some cases this requires lifestyle

changes or different ways of doing things to bring about progress,

but as the Chinese philosopher Lao Tsu wrote, “A journey of a

thousand miles must begin with a single step.”

driven by globalization of information management, has dou-

bled the number of vehicles on the roads, threatening this prog-

ress. Still, the gains made in Delhi are encouraging for people

everywhere. Twenty years ago, Cubatao, Brazil, was described as the “Val-

ley of Death,” one of the most dangerously polluted places in the

world. Every year a steel plant, a huge oil refinery, and fertilizer

and chemical factories churned out thousands of tons of air pol-

lutants that were trapped between onshore winds and the uplifted

plateau on which São Paulo sits ( fig. 16.30 ). Trees died on the

surrounding hills. Birth defects and respiratory diseases were

alarmingly high. Since then, however, the citizens of Cubatao

have made remarkable progress in cleaning up their environment.

The end of military rule and restoration of democracy allowed

residents to publicize their complaints. The environment became

an important political issue. The state of São Paulo invested about

$100 million and the private sector spent twice as much to clean

up most pollution sources in the valley. Particulate pollution was

reduced 75 percent, ammonia emissions were reduced 97 percent,

hydrocarbons that cause ozone and smog were cut 86 percent, and

sulfur dioxide production fell 84 percent. Fish are returning to the

rivers, and forests are regrowing on the mountains. Progress is

possible! We hope that similar success stories will be obtainable

elsewhere.